text: /*
   * Copyright (c) 2006 The Regents of The University of Michigan
   * Copyright (c) 2013 Advanced Micro Devices, Inc.
   * Copyright (c) 2013 Mark D. Hill and David A. Wood
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions are
   * met: redistributions of source code must retain the above copyright
   * notice, this list of conditions and the following disclaimer;
   * redistributions in binary form must reproduce the above copyright
   * notice, this list of conditions and the following disclaimer in the
   * documentation and/or other materials provided with the distribution;
   * neither the name of the copyright holders nor the names of its
   * contributors may be used to endorse or promote products derived from
   * this software without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
   * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
   * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
   * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
   * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
   * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
   * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   *
   * Authors: Nathan Binkert
   *          Steve Reinhardt
   */
  
  #include "sim/simulate.hh"
  
  #include <mutex>
  #include <thread>
  
  #include "base/logging.hh"
  #include "base/pollevent.hh"
  #include "base/types.hh"
  #include "sim/async.hh"
  #include "sim/eventq_impl.hh"
  #include "sim/sim_events.hh"
  #include "sim/sim_exit.hh"
  #include "sim/stat_control.hh"
  
  //! Mutex for handling async events.
  std::mutex asyncEventMutex;
  
  //! Global barrier for synchronizing threads entering/exiting the
  //! simulation loop.
  Barrier *threadBarrier;
  
  //! forward declaration
  Event *doSimLoop(EventQueue *);
  
  /**
   * The main function for all subordinate threads (i.e., all threads
   * other than the main thread).  These threads start by waiting on
   * threadBarrier.  Once all threads have arrived at threadBarrier,
   * they enter the simulation loop concurrently.  When they exit the
   * loop, they return to waiting on threadBarrier.  This process is
   * repeated until the simulation terminates.
   */
  static void
  thread_loop(EventQueue *queue)
  {
      while (true) {
          threadBarrier->wait();
          doSimLoop(queue);
      }
  }
  
  GlobalSimLoopExitEvent *simulate_limit_event = nullptr;
  
  /** Simulate for num_cycles additional cycles.  If num_cycles is -1
   * (the default), do not limit simulation; some other event must
   * terminate the loop.  Exported to Python.
   * @return The SimLoopExitEvent that caused the loop to exit.
   */
  GlobalSimLoopExitEvent *
  simulate(Tick num_cycles)
  {
      // The first time simulate() is called from the Python code, we need to
      // create a thread for each of event queues referenced by the
      // instantiated sim objects.
      static bool threads_initialized = false;
      static std::vector<std::thread *> threads;
  
      if (!threads_initialized) {
          threadBarrier = new Barrier(numMainEventQueues);
  
          // the main thread (the one we're currently running on)
          // handles queue 0, so we only need to allocate new threads
          // for queues 1..N-1.  We'll call these the "subordinate" threads.
          for (uint32_t i = 1; i < numMainEventQueues; i++) {
              threads.push_back(new std::thread(thread_loop, mainEventQueue[i]));
          }
  
          threads_initialized = true;
          simulate_limit_event =
              new GlobalSimLoopExitEvent(mainEventQueue[0]->getCurTick(),
                                         "simulate() limit reached", 0);
      }
  
      inform("Entering event queue @ %d.  Starting simulation...\n", curTick());
  
      if (num_cycles < MaxTick - curTick())
          num_cycles = curTick() + num_cycles;
      else // counter would roll over or be set to MaxTick anyhow
          num_cycles = MaxTick;
  
      simulate_limit_event->reschedule(num_cycles);
  
      GlobalSyncEvent *quantum_event = NULL;
      if (numMainEventQueues > 1) {
          if (simQuantum == 0) {
              fatal("Quantum for multi-eventq simulation not specified");
          }
  
          quantum_event = new GlobalSyncEvent(curTick() + simQuantum, simQuantum,
                              EventBase::Progress_Event_Pri, 0);
  
          inParallelMode = true;
      }
  
      // all subordinate (created) threads should be waiting on the
      // barrier; the arrival of the main thread here will satisfy the
      // barrier, and all threads will enter doSimLoop in parallel
      threadBarrier->wait();
      Event *local_event = doSimLoop(mainEventQueue[0]);
      assert(local_event != NULL);
  
      inParallelMode = false;
  
      // locate the global exit event and return it to Python
      BaseGlobalEvent *global_event = local_event->globalEvent();
      assert(global_event != NULL);
  
      GlobalSimLoopExitEvent *global_exit_event =
          dynamic_cast<GlobalSimLoopExitEvent *>(global_event);
      assert(global_exit_event != NULL);
  
      //! Delete the simulation quantum event.
      if (quantum_event != NULL) {
          quantum_event->deschedule();
          delete quantum_event;
      }
  
      return global_exit_event;
  }
  
  /**
   * Test and clear the global async_event flag, such that each time the
   * flag is cleared, only one thread returns true (and thus is assigned
   * to handle the corresponding async event(s)).
   */
  static bool
  testAndClearAsyncEvent()
  {
      bool was_set = false;
      asyncEventMutex.lock();
  
      if (async_event) {
          was_set = true;
          async_event = false;
      }
  
      asyncEventMutex.unlock();
      return was_set;
  }
  
  /**
   * The main per-thread simulation loop. This loop is executed by all
   * simulation threads (the main thread and the subordinate threads) in
   * parallel.
   */
  Event *
  doSimLoop(EventQueue *eventq)
  {
      // set the per thread current eventq pointer
      curEventQueue(eventq);
      eventq->handleAsyncInsertions();
  
      while (1) {
          // there should always be at least one event (the SimLoopExitEvent
          // we just scheduled) in the queue
          assert(!eventq->empty());
          assert(curTick() <= eventq->nextTick() &&
                 "event scheduled in the past");
  
          if (async_event && testAndClearAsyncEvent()) {
              // Take the event queue lock in case any of the service
              // routines want to schedule new events.
              std::lock_guard<EventQueue> lock(*eventq);
              if (async_statdump || async_statreset) {
                  Stats::schedStatEvent(async_statdump, async_statreset);
                  async_statdump = false;
                  async_statreset = false;
              }
  
              if (async_io) {
                  async_io = false;
                  pollQueue.service();
              }
  
              if (async_exit) {
                  async_exit = false;
                  exitSimLoop("user interrupt received");
              }
  
              if (async_exception) {
                  async_exception = false;
                  return NULL;
              }
          }
  
          Event *exit_event = eventq->serviceOne();
          if (exit_event != NULL) {
              return exit_event;
          }
      }
  
      // not reached... only exit is return on SimLoopExitEvent
  }
  